The health consequences of quitting smoking are well established; despite this, over one-fourth of all adults in the United States will smoke. One of the many reinforcing qualities of cigarette smoking is weight control. Despite the importance of determining the mechanisms of weight gain following smoking cessation, very little is known regarding the dietary, activity, or metabolic changes associated with smoking cessation. A recent review concluded that there is tremendous inconsistency in the literature regarding whether the causes of postcessation weight gain are largely metabolic, dietary, or a combination of metabolic and dietary factors. These inconsistent findings have led investigators to search for moderator variables that may interact with the dietary, metabolic, and weight changes associated with smoking cessation. Two variables that are highly likely to interact with smoking cessation and postcessation weight gain are smoking rate and gender. It is clear that females enjoy more of the weight control "benefits" of smoking, they metabolize nicotine slower, and may be at greater risk of dietary-induced postcessation weight gain than males. Additionally, moderate smokers, relative to either light or heavy smokers, have a greater weight suppression effect from smoking and there is recent evidence that metabolic rates of moderate smokers rise following smoking cigarettes while the metabolic rates of heavy smokers are more likely to decrease following smoking. However, no study has systematically evaluated the effects of gender and smoking rate on smoking-cessation related changes in body weight and energy balance in a sample of individuals who quit smoking versus those randomly assigned to continued smoking. We propose the following: (1) To determine if the changes in the energy balance equation (viz., changes in dietary intake, physical activity, resting energy expenditure, and body weight) occur following smoking cessation and; (2) To determine if changes in energy balance following cessation vary as a function of subject smoking rat, race, and gender.